The present invention relates to systems, devices and methods for transforming between a view orientation with respect to a virtual point external to a patient or with respect to an axis along which the virtual point is viewed and a view orientation with respect to a target point or with respect to an axis along which the target point is viewed for navigation purposes. The invention also relates to a device-readable medium embodying a program of instructions (i.e., software) for implementing the transformation method(s).
Image-guided surgery generally involves: (1) acquiring 2-D images, either preoperatively or intraoperatively, of internal anatomical structures of interest, e.g., of a patient target site; (2) reformating a 2-D image or reconstructing a 3-D image based on the acquired 2-D images; (3) segmenting the images; (4) registering the patient to the images; (4) targeting a site of interest in the patient; and (5) navigating to that point.
Typically, the acquired 2-D images are reformated to generate two additional sets of 2-D images. One of the sets of images is parallel to a first plane defined by two of the three axes in a 3-D coordinate system, say, the xy-plane; a second set is parallel to, say, the xz-plane; and a third set is parallel to, say, the yz-plane.
Registration between the patient and the image provides a basis by which a medical instrument, such as an endoscope, can be tracked in the images as it is moved within the operating field during surgery.
Registration is the point-for-point mapping of one space to another allowing corresponding points to be mapped together. Corresponding points are those points that represent the same anatomical features in two spaces. There are multiple registration algorithms, such as fiducial based, intensity based and entropy based, that can be used to register two spaces, such as image-to-image and image-to-physical. For example, a fiducial based, image-to-physical algorithm uses as input the 3-D positions of three or more fiducial markers in both spaces, and outputs the point-for-point mapping from one space to another. The mapping addresses the physical differences in position of the two spaces, which consists of a shift, rotation, scale or any combination thereof. The correct mapping, or registration, is the particular rotation, shift or scale that will map all the localized fiducial positions in one 3-D space, for example, the physical space around the patient in the operating room, to the corresponding localized positions in the second space, for example, a CT image. If these fiducial positions are properly mapped then, unless there is distortion in the images, all non-fiducial points in the first space will be mapped to corresponding points in the second space as well. These non-fiducial points are the anatomical points of interest to the surgeon. Because of inevitable small errors in the localization of the fiducial points, it is rarely possible to find a rotation, shift or scale that will map all fiducial points exactly from one space to the other. Therefore, an algorithm is used that finds the rotation, shift or scale that will produce the smallest fiducial mapping error (in the standard least-squares sense). This mapping error provides a measure of the success of the registration. It is computed by first calculating, for each fiducial point the distance between its localized position in the second space and the localized position in the first space as mapped into the second space. The mapping error is then computed by calculating the square root of the average of the squares of these distances.
With registration established, the endoscope can be tracked relative to the internal structures of the patient as it is navigated in and around the patient target site during surgery. Images of the target site are displayed to assist the user (e.g., surgeon) in navigating to the target site. Current methods of tracking include the use of robotic or mechanical arms, or optical, sonic or magnetic devices. Tracking may be based on, for example, the known mathematics of xe2x80x9ctriangulation.xe2x80x9d
Further details regarding techniques involved in image-guided surgery are disclosed in g U.S. application Ser. No. 08/884,289, entitled xe2x80x9cMethod and Apparatus for Volumetric Image Navigation,xe2x80x9d filed Jun. 27, 1997, now abandoned and international application, publication no.: WO 99/00052, publication date: Jan. 7, 1999. U.S. application Ser. No. 09/411,363, filed Sept. 30, 1999, now U.S. Pat. No. 6,167,296 is a continuation of U.S. application Ser. No. 08/884,209. The contents of each of these applications are incorporated herein by reference.
One of the problems with conventional navigation systems is that usually the endoscope has a limited range of movement once inside the patient. This, in turn, limits the view orientations with which the target site may be viewed. For example, it is usually not possible to move the endoscope even 20xc2x0 one way or the other with respect to a point in the target site to obtain views from those perspectives, and it is almost never possible to move the endoscope 180xc2x0 to view the target site from the other side. This significantly limits the information available to the surgeon.
The present invention overcomes this problem by providing systems and methods for obtaining view information of a patient target site that is independent of the range of movement of a medical instrument, such as an endoscope.
In one aspect of the invention, an apparatus is provided for use in an image-guided surgical or a diagnostic procedure at an internal target site of a patient. The apparatus comprises:
(a) a data-storage medium for storing scan data representing internal scans of the patient target site;
(b) an instrument defining a view axis, where the instrument is adapted to be moved to a selected orientation with respect to the patient target site;
(c) means for tracking the orientation of the instrument with respect to the patient target site as the instrument is moved;
(d) a display device; and
(e) a processor in communication with the data storage medium, the tracking means, and the display device, for carrying out steps (i)-(iii) in a first mode of operation, and steps (iv)-(viii) in a second mode of operation.
The first mode of operation includes: (i) determining the orientation of the instrument view axis with respect to the patient target site, as the instrument is moved to a selected orientation with respect to the patient target site; (ii) using at least some of the scan data to construct an image of the patient target site, as viewed with respect to the orientation of the instrument; and (iii) displaying the image on the display device.
The second mode of operation includes: (iv) receiving input that indicates a selected orientation at which a virtual target point, external to the patient, is being viewed; (v) determining, from the input, the selected view orientation with respect to the virtual target point; (vi) transforming the view orientation determined in step (v) to a view orientation with respect to the selected patient target point; (vii) using the scan data to construct an image of the patient target site, as viewed along the transformed view orientation generated in step (vi); and (viii) displaying the image generated in step (vii) on the display device.